/*******************************************************************************
* Copyright (c) 2003, 2005 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.draw2d.graph;
/**
* This visitor eliminates cycles in the graph via a modified implementation of the
* greedy cycle removal algorithm for directed graphs. The algorithm has been modified to
* handle the presence of Subgraphs and compound cycles which may result. This algorithm
* determines a set of edges which can be inverted and result in a graph without compound
* cycles.
*
* @author Daniel Lee
* @author Randy Hudson
* @since 2.1.2
*/
class CompoundBreakCycles extends GraphVisitor {
/*
* Caches all nodes in the graph. Used in identifying cycles and in cycle removal.
* Flag field indicates "presence". If true, the node has been removed from the list.
*/
private NodeList graphNodes;
private NodeList sL = new NodeList();
private boolean allFlagged(NodeList nodes) {
for (int i = 0; i < nodes.size(); i++) {
if (nodes.getNode(i).flag == false)
return false;
}
return true;
}
private int buildNestingTreeIndices(NodeList nodes, int base) {
for (int i = 0; i < nodes.size(); i++) {
Node node = (Node)nodes.get(i);
if (node instanceof Subgraph) {
Subgraph s = (Subgraph)node;
s.nestingTreeMin = base;
base = buildNestingTreeIndices(s.members, base);
}
node.nestingIndex = base++;
}
return base++;
}
private boolean canBeRemoved(Node n) {
return !n.flag && getChildCount(n) == 0;
}
private boolean changeInDegree(Node n, int delta) {
return (n.workingInts[1] += delta) == 0;
}
private boolean changeOutDegree(Node n, int delta) {
return (n.workingInts[2] += delta) == 0;
}
/*
* Execution of the modified greedy cycle removal algorithm.
*/
private void cycleRemove(NodeList children) {
NodeList sR = new NodeList();
do {
findSinks(children, sR);
findSources(children);
// all sinks and sources added, find node with highest
// outDegree - inDegree
Node max = findNodeWithMaxDegree(children);
if (max != null) {
for (int i = 0; i < children.size(); i++) {
Node child = (Node)children.get(i);
if (child.flag)
continue;
if (child == max)
restoreSinks(max, sR);
else
restoreSources(child);
}
remove(max);
}
} while (!allFlagged(children));
while (!sR.isEmpty())
sL.add(sR.remove(sR.size() - 1));
}
private void findInitialSinks(NodeList children, NodeList sinks) {
for (int i = 0; i < children.size(); i++) {
Node node = children.getNode(i);
if (node.flag)
continue;
if (isSink(node) && canBeRemoved(node)) {
sinks.add(node);
node.flag = true;
}
if (node instanceof Subgraph)
findInitialSinks(((Subgraph)node).members, sinks);
}
}
private void findInitialSources(NodeList children, NodeList sources) {
for (int i = 0; i < children.size(); i++) {
Node node = children.getNode(i);
if (isSource(node) && canBeRemoved(node)) {
sources.add(node);
node.flag = true;
}
if (node instanceof Subgraph)
findInitialSources(((Subgraph)node).members, sources);
}
}
private Node findNodeWithMaxDegree(NodeList nodes) {
int max = Integer.MIN_VALUE;
Node maxNode = null;
for (int i = 0; i < nodes.size(); i++) {
Node node = nodes.getNode(i);
if (node.flag)
continue;
int degree = getNestedOutDegree(node) - getNestedInDegree(node);
if (degree >= max && node.flag == false) {
max = degree;
maxNode = node;
}
}
return maxNode;
}
/*
* Finds all sinks in graphNodes and adds them to the passed NodeList
*/
private void findSinks(NodeList children, NodeList rightList) {
// NodeList rightList = new NodeList();
NodeList sinks = new NodeList();
findInitialSinks(children, sinks);
while (!sinks.isEmpty()) {
Node sink = sinks.getNode(sinks.size() - 1);
rightList.add(sink);
sinks.remove(sink);
removeSink(sink, sinks);
// Check to see if the removal has made the parent node a sink
if (sink.getParent() != null) {
Node parent = sink.getParent();
setChildCount(parent, getChildCount(parent) - 1);
if (isSink(parent) && canBeRemoved(parent)) {
sinks.add(parent);
parent.flag = true;
}
}
}
}
/*
* Finds all sources in graphNodes and adds them to the sL NodeList.
*/
private void findSources(NodeList children) {
NodeList sources = new NodeList();
findInitialSources(children, sources);
while (!sources.isEmpty()) {
Node source = sources.getNode(sources.size() - 1);
sL.add(source);
sources.remove(source);
removeSource(source, sources);
// Check to see if the removal has made the parent node a source
if (source.getParent() != null) {
Node parent = source.getParent();
setChildCount(parent, getChildCount(parent) - 1);
if (isSource(parent) && canBeRemoved(parent)) {
sources.add(parent);
parent.flag = true;
}
}
}
}
private int getChildCount(Node n) {
return n.workingInts[3];
}
private int getInDegree(Node n) {
return n.workingInts[1];
}
private int getNestedInDegree(Node n) {
int result = getInDegree(n);
if (n instanceof Subgraph) {
Subgraph s = (Subgraph)n;
for (int i = 0; i < s.members.size(); i++)
if (!s.members.getNode(i).flag)
result += getInDegree(s.members.getNode(i));
}
return result;
}
private int getNestedOutDegree(Node n) {
int result = getOutDegree(n);
if (n instanceof Subgraph) {
Subgraph s = (Subgraph)n;
for (int i = 0; i < s.members.size(); i++)
if (!s.members.getNode(i).flag)
result += getOutDegree(s.members.getNode(i));
}
return result;
}
private int getOrderIndex(Node n) {
return n.workingInts[0];
}
private int getOutDegree(Node n) {
return n.workingInts[2];
}
private void initializeDegrees(DirectedGraph g) {
g.nodes.resetFlags();
g.edges.resetFlags(false);
for (int i = 0; i < g.nodes.size(); i++) {
Node n = g.nodes.getNode(i);
setInDegree(n, n.incoming.size());
setOutDegree(n, n.outgoing.size());
if (n instanceof Subgraph)
setChildCount(n, ((Subgraph)n).members.size());
else
setChildCount(n, 0);
}
}
private void invertEdges(DirectedGraph g) {
// Assign order indices
int orderIndex = 0;
for (int i = 0; i < sL.size(); i++) {
setOrderIndex(sL.getNode(i), orderIndex++);
}
// Invert edges that are causing a cycle
for (int i = 0; i < g.edges.size(); i++) {
Edge e = g.edges.getEdge(i);
if (getOrderIndex(e.source) > getOrderIndex(e.target)
&& !e.source.isNested(e.target)
&& !e.target.isNested(e.source)) {
e.invert();
e.isFeedback = true;
}
}
}
/**
* Removes all edges connecting the given subgraph to other nodes outside of it.
* @param s
* @param n
*/
private void isolateSubgraph(Subgraph subgraph, Node member) {
Edge edge = null;
for (int i = 0; i < member.incoming.size(); i++) {
edge = member.incoming.getEdge(i);
if (!subgraph.isNested(edge.source) && !edge.flag)
removeEdge(edge);
}
for (int i = 0; i < member.outgoing.size(); i++) {
edge = member.outgoing.getEdge(i);
if (!subgraph.isNested(edge.target) && !edge.flag)
removeEdge(edge);
}
if (member instanceof Subgraph) {
NodeList members = ((Subgraph)member).members;
for (int i = 0; i < members.size(); i++)
isolateSubgraph(subgraph, members.getNode(i));
}
}
private boolean isSink(Node n) {
return getOutDegree(n) == 0
&& (n.getParent() == null
|| isSink(n.getParent()));
}
private boolean isSource(Node n) {
return getInDegree(n) == 0
&& (n.getParent() == null
|| isSource(n.getParent()));
}
private void remove(Node n) {
n.flag = true;
if (n.getParent() != null)
setChildCount(n.getParent(), getChildCount(n.getParent()) - 1);
removeSink(n, null);
removeSource(n, null);
sL.add(n);
if (n instanceof Subgraph) {
Subgraph s = (Subgraph)n;
isolateSubgraph(s, s);
cycleRemove(s.members);
}
}
private boolean removeEdge(Edge e) {
if (e.flag)
return false;
e.flag = true;
changeOutDegree(e.source, -1);
changeInDegree(e.target, -1);
return true;
}
/**
* Removes all edges between a parent and any of its children or descendants.
*/
private void removeParentChildEdges(DirectedGraph g) {
for (int i = 0; i < g.edges.size(); i++) {
Edge e = g.edges.getEdge(i);
if (e.source.isNested(e.target) || e.target.isNested(e.source))
removeEdge(e);
}
}
private void removeSink(Node sink, NodeList allSinks) {
for (int i = 0; i < sink.incoming.size(); i++) {
Edge e = sink.incoming.getEdge(i);
if (!e.flag) {
removeEdge(e);
Node source = e.source;
if (allSinks != null && isSink(source) && canBeRemoved(source)) {
allSinks.add(source);
source.flag = true;
}
}
}
}
private void removeSource(Node n, NodeList allSources) {
for (int i = 0; i < n.outgoing.size(); i++) {
Edge e = n.outgoing.getEdge(i);
if (!e.flag) {
e.flag = true;
changeInDegree(e.target, -1);
changeOutDegree(e.source, -1);
Node target = e.target;
if (allSources != null && isSource(target) && canBeRemoved(target)) {
allSources.add(target);
target.flag = true;
}
}
}
}
/**
* Restores an edge if it has been removed, and both of its nodes are not removed.
* @param e the edge
* @return <code>true</code> if the edge was restored
*/
private boolean restoreEdge(Edge e) {
if (!e.flag || e.source.flag || e.target.flag)
return false;
e.flag = false;
changeOutDegree(e.source, 1);
changeInDegree(e.target, 1);
return true;
}
/**
* Brings back all nodes nested in the given node.
* @param node the node to restore
* @param sr current sinks
*/
private void restoreSinks(Node node, NodeList sR) {
if (node.flag && sR.contains(node)) {
node.flag = false;
if (node.getParent() != null)
setChildCount(node.getParent(), getChildCount(node.getParent()) + 1);
sR.remove(node);
for (int i = 0; i < node.incoming.size(); i++) {
Edge e = node.incoming.getEdge(i);
restoreEdge(e);
}
for (int i = 0; i < node.outgoing.size(); i++) {
Edge e = node.outgoing.getEdge(i);
restoreEdge(e);
}
}
if (node instanceof Subgraph) {
Subgraph s = (Subgraph)node;
for (int i = 0; i < s.members.size(); i++) {
Node member = s.members.getNode(i);
restoreSinks(member, sR);
}
}
}
/**
* Brings back all nodes nested in the given node.
* @param node the node to restore
* @param sr current sinks
*/
private void restoreSources(Node node) {
if (node.flag && sL.contains(node)) {
node.flag = false;
if (node.getParent() != null)
setChildCount(node.getParent(), getChildCount(node.getParent()) + 1);
sL.remove(node);
for (int i = 0; i < node.incoming.size(); i++) {
Edge e = node.incoming.getEdge(i);
restoreEdge(e);
}
for (int i = 0; i < node.outgoing.size(); i++) {
Edge e = node.outgoing.getEdge(i);
restoreEdge(e);
}
}
if (node instanceof Subgraph) {
Subgraph s = (Subgraph)node;
for (int i = 0; i < s.members.size(); i++) {
Node member = s.members.getNode(i);
restoreSources(member);
}
}
}
public void revisit(DirectedGraph g) {
for (int i = 0; i < g.edges.size(); i++) {
Edge e = g.edges.getEdge(i);
if (e.isFeedback())
e.invert();
}
}
private void setChildCount(Node n, int count) {
n.workingInts[3] = count;
}
private void setInDegree(Node n, int deg) {
n.workingInts[1] = deg;
}
private void setOrderIndex(Node n, int index) {
n.workingInts[0] = index;
}
private void setOutDegree(Node n, int deg) {
n.workingInts[2] = deg;
}
/**
* @see GraphVisitor#visit(org.eclipse.draw2d.graph.DirectedGraph)
*/
public void visit(DirectedGraph g) {
initializeDegrees(g);
graphNodes = g.nodes;
NodeList roots = new NodeList();
for (int i = 0; i < graphNodes.size(); i++) {
if (graphNodes.getNode(i).getParent() == null)
roots.add(graphNodes.getNode(i));
}
buildNestingTreeIndices(roots, 0);
removeParentChildEdges(g);
cycleRemove(roots);
invertEdges(g);
}
}